Frequency translating receivers, and in particular superheterodyne receivers, are widely employed in communication transceivers, test and measurement instruments, and other systems.
FIG. 1 shows a functional block diagram of a generalized example of a frequency translating receiver, in particular a superheterodyne receiver 10. Receiver 10 includes a radio frequency (RF) front end section 2, a frequency converter 4, an intermediate frequency (IF) filter section 6, a demodulator 8, and a baseband amplifier 9.
In the example receiver 10, RF front end section 2 includes an RF filter (sometimes called a preselector) 11 and an RF amplifier 12. Frequency converter 4 includes a local oscillator (LO) 13, a LO filter 14, and a mixer 15. IF filter section 6 includes an IF filter 16 and an IF amplifier 17.
It should be understood that many elements shown in FIG. 1 may be omitted in other embodiments. For example, in other embodiments one or both components of RF front end section 2 may be omitted, LO filter 14 may be omitted, IF filter 16 and IF amplifier 17 may be combined, and/or IF amplifier 17 may be omitted. In some embodiments, the output of IF filter section 6 may be digitized by an analog-to-digital converter (ADC) and demodulation may be performed digitally, for example by a digital signal processor (DSP). In that case, demodulator 8 and baseband amplifier 9 may be replaced by an ADC and a DSP. Many variations are common.
In operation, receiver 10 receives an RF input signal RF IN at an input terminal or input port 1, and outputs a baseband output signal (e.g., digital data) at an output port 3. The details of the operation of a superheterodyne receiver such as receiver 10 is very well known to those skilled in the art, and in the interest of brevity will not be explained here.
In many situations, it is desired to be able to efficiently and accurately characterize the IF response of a frequency translating receiver such as receiver 10. In particular, in some cases it may be desired to efficiently and accurately characterize the IF phase dispersion characteristics of a frequency translating receiver such as receiver 10. For example, characterization of the IF phase dispersion may be necessary for a signal analyzer in order to make accurate vector signal analyzer measurements, e.g., to measure error-vector-magnitude (EVM). Here, given a frequency range defined by a lower IF frequency and an upper IF frequency, the phase dispersion of an IF channel over the given frequency range is defined as the deviation of the phase of the IF channel at the middle of the frequency range, from the average phase over the frequency range between the lower and upper IF frequency.
Thus it would be desirable to provide a method and system to characterize the IF phase dispersion characteristics of a frequency translating receiver, in particular a superheterodyne receiver.